Parallel Sub-Workflow Execution with Wait-for-All Pattern

This workflow template demonstrates a powerful design pattern for executing multiple instances of a sub-workflow in parallel, asynchronously, rather than sequentially. It splits incoming data (e.g., a list of documents) into parallel sub-workflow calls, each receiving a unique identifier and the parent workflow's resume URL. The sub-workflows process independently and send a callback to the parent upon completion, allowing the main workflow to proceed only after all have finished.

The core mechanism involves a 'wait-for-all' loop using an IF node to check completion status, building a unique list of reported identifiers from callbacks received via a webhook. This eliminates the need for external tools like databases or messaging queues, keeping everything self-contained in n8n. Setup requires configuring the sub-workflow to POST callbacks with its ID when done.

Benefits include massive time savings for batch processing, improved scalability for high-volume tasks, and simplified orchestration without custom code. Use cases: parallel document processing, multi-API calls, image/video batch handling, or any data-driven task where sequential execution is a bottleneck.